1. Field of the Invention
The present invention is directed to low surface energy polyisocyanate addition compounds which contain ethylenically unsaturated groups, urethane groups and fluorine and to their use in coating compositions curable by free radical polymerization.
2. Description of Related Art
Polyisocyanate addition compounds, which contain ethylenically unsaturated groups, are prepared by the reaction of polyisocyanates with isocyanate-reactive compounds containing ethylenically unsaturated groups, and cure by free radical polymerization, are well known.
Although coatings prepared from these compositions possess many valuable properties, one property, in particular, which needs to be improved is the surface quality. It can be difficult to formulate coating compositions to obtain a coating having a smooth surface as opposed to one containing surface defects such as craters, etc.
It is believed that these difficulties are related to the high surface tension of the polyisocyanate addition compounds. Another problem caused by the high surface tension is the difficulty in cleaning the coatings. Regardless of their potential application area, there is a high likelihood that the coatings will be subjected to stains, graffiti, etc.
The incorporation of either fluorine or siloxane groups into polyisocyanates via allophanate groups in order to reduce the surface tension of the polyisocyanates and the surface energy of the resulting polyurethane coatings is disclosed in U.S. Pat. Nos. 5,541,281; 5,574,122; 5,576,411; 5,646,227; 5,691,439; and 5,747,629. During the cure of one-component and two-component coating compositions containing these polyisocyanates, which is relatively slow at room temperature and even at elevated temperatures, the polyisocyanate molecules containing fluorine or siloxane groups rise to the surface of the coating before being locked into position by urethane formation resulting in a low surface energy.
Polyisocyanate addition compounds containing ethylenically unsaturated groups and fluorine are disclosed in two articles by Du et al and Liu et al from the Chinese Journal of Chemistry (2003), 21(6), 698-705 and (2001), 19(4), 386-393; Japanese Patent No. 2000103824; Bongiovanni et al, Progress in Organic Coatings, (1999), 36(1-2), 70-78; U.S. Pat. Nos. 5,446,118 and 5,144,056. All of these references describe the preparation of polyaddition compounds from diisocyanate monomers.
Polyisocyanate addition compounds containing ethylenically unsaturated groups and fluorine are also disclosed in U.S. Pat. No. 6,746,812 and Japanese Patent No. 2996150. In these patents the polyisocyanate addition products were prepared from polyisocyanate adducts containing urethane groups. Finally, in U.S. Pat. No. 6,906,115 polyisocyanate addition products containing ethylenically unsaturated groups and fluorine were prepared from polyisocyanate trimers.
It is an object of the present invention to provide polyisocyanate addition compounds which have reduced surface tension and, thus, are suitable for the production of coatings which have lower surface energies, improved surfaces and improved cleanability and which also possess the other valuable properties of the known coatings prepared from ethylenically unsaturated compounds.
These objectives may be achieved with the polyisocyanate addition compounds of the present invention containing ethylenically unsaturated groups, urethane groups and fluorine which are described hereinafter. It is surprising that coatings obtained from these polyisocyanates have low surface energies. Because of the rapid cure that these coatings undergo during free radical polymerization, it would be expected that the fluorine-containing molecules would be trapped below the surface and, thus, would not be able to provide coatings having low surface energies.